Asphalt binders or cements are used in a wide variety of paving products. For example, some asphalt binders are used together with an aggregate to produce a pavement material, while other asphalt binders are used without aggregate to seal or coat surfaces.
Asphalt binders generally comprise residue from commonly used petroleum refining processes. In many asphalt binders, property-enhancing additives are added to the residue in order to alter the properties of the asphalt binder. In addition, in some cases, the asphalt binder is emulsified prior to use. The emulsification process reduces the temperature at which an asphalt binder can be utilized by reducing the handling viscosity of the asphalt binder. The emulsification typically uses a high shear colloid mill or other mechanical equipment that is capable of reducing the bulk asphalt liquid to very small particles (typically 4 to 20 micrometers). The emulsification requires the asphalt binder to be at a temperature where the viscosity can be processed by the available equipment. A surfactant solution is used that is capable of dispersing the fine asphalt particles of the binder into the surfactant solution and maintaining the asphalt particles in the dispersed state indefinitely at temperatures above freezing.
A large variety of property-enhancing additives may be used to alter the properties of the asphalt binder depending on the desired application. Some property-enhancing additives react with the asphalt to affect the properties of the base asphalt material, producing a modified asphalt. For example, certain polymers may be added to the asphalt binder, producing a polymer-modified asphalt (PMA) binder. In other examples, certain acids are added to the asphalt binder, producing an acid-modified asphalt binder. In some instances, emulsifying such modified asphalt binders presents unique challenges, both in maintaining an emulsion and in maintaining the properties of the modified asphalt binder after emulsification.